Occupational Ergonomics. Theory and Applications. Bhattacharya A, McGlothlin JD, eds., New York: Marcel Dekker, 1996 Apr; :403-416
The usual concept of the normal workday is an 8-hour period occurring during the daytime; all other schedules are often viewed as abnormal, unusual, or unnatural. The challenges an individual faces when working outside "normal" hours are complex and multidimensional. Yet, extended and around-the-clock services are rapidly becoming a fact of life for many industries and workers. Work schedules encompassing hours other than daytime are becoming more, not less, prevalent for a greater number of workers. The notion of a "nine-to-five" work schedule may well be a thing of the past. The term shiftwork is often applied to sthedules that include hours of work other than daytime, but there is no universally accepted definition of the tenn. The most comprehensive estimate of the prevalence of shiftwork in the United States is based on the 1991 Current Population Survey, a household sample survey conducted monthly by the Bureau of the Census. The data indicated that of the 80.5 million full-time wage and salary employees, about 18%, or 14.5 million people, had work schedules that differed from daytime hours. Of the 18%, evening schedules were most prevalent at 5.1%, night shifts and "employer-arranged irregular schedules" followed, each at 3.7%, and rotating shifts were reponed for 3.4% of total workers. The reasons for around-the-clock hours of work are varied. Economic factors such as recouping a large capital investment on equipment, production cycle time, a high demand for products and services, or lower utility costs during non-peak usage hours may force 24-h operations. Shiftwork is also prevalent in various transponation-related occupations including trucking, railroad, airlines, and shipping. The business concept of just-in-time manufacturing requires a continual movement of product and raw materials. With an increasingly mobile society, airline flights at all hours of the day are extremely convenient for transponing both passengers and freight. As a society, we are demanding that more services be available on a 24-h basis. Constant medical, police, and fire protection are a requirement in our contemporary society. We realize the merit of grocery and drug stores, gas stations, and convenience stores that are open 24 h a day. During our relaxation periods, we enjoy having restaurants, entertainment, and recreational activities available at any time of the day or night. Nevertheless, in order to accommodate us, someone else must be at work to provide the services we desire! For the individual, shiftwork can have biological, psychological, or social effects with both short- and long-term consequences. It is not possible within the confines of this chapter to provide an in-depth discussion of every variable that might affect a shiftworker. Those who wish to explore a particular issue in more detail should consult other reviews. The purpose of this chapter is to highlight some of these issues and to alert the reader to things to think about when implementing or evaluating work schedules.